The present disclosure relates to an application system, e.g., for the in series application of a high viscosity coating material such as, for example, sealing, adhesive, insulating or similar material. In addition, the present disclosure relates to a corresponding application robot and a corresponding applicator for this system.
When coating workpieces such as for example vehicle bodies or parts thereof with coating compositions such as sealants, for example for seam sealing, or adhesives or preservatives such as for example wax or laminating agents or indeed insulating materials etc., in many cases metering of the material fed to the applicator needs to be as precise as possible. The viscosity of such coating compositions, for which the applicator of an exemplary system is intended to be suitable, is significantly greater than for example the viscosity of liquid paint measured using the same measurement method. If for example using the measurement method standardised to standard series DIN 53019 the viscosity of water-based paints is measured, which in accordance with the thixotropic behaviour of such coating materials is to a considerable extent dependent on the shear rate, typical values of between 50 and around 200 mPas (at 20° C.) are obtained for example for a shear rate (flow rate of the measurement sample relative to the width of a shear gap in which the liquid flows) of 1000/s. The coating compositions to be applied according to the exemplary illustrations herein have, in contrast, a correspondingly measured viscosity of more than 300 mPas, typically more than 500 mPas. The likewise thixotropic material used for vehicle bodies for sealing and the other stated purposes may for example typically have a viscosity measured using the stated method of 1.5 Pas to 7 Pas (or more than twice these values, if the shear rate amounts to just 100/s for example, instead of 1000/s). The applicator of the application system according to the exemplary illustrations herein is intended to be suitable for coating material the viscosity of which, measured using the same measurement method, amounts to, in some illustrations, at least 5 times, in particular at least 7 times, the viscosity of liquid paint such as especially the paints conventional in vehicle painting.
The conventional paint atomisers such as for example a rotary atomiser with built-in metering gear pump (DE 10115463 A1) are not suitable for application of the high viscosity coating compositions here under consideration in particular for vehicle bodies. Instead, a particularly suitable method for applying sealing seams is the “airless spraying method”, in which, in contrast to rotary atomisation or air atomisation of paint, the material is atomised at the application nozzle by the material pressure alone. For the exemplary illustrations, however, known air-assisted applicators are also suitable for large-area material application, as is necessary for underbody sealant application or for spraying of insulation material. A factor common to the different applicators suitable according to the present disclosure is that they operate with significantly higher material pressure than conventional paint atomisers, wherein the material pressure at the application nozzle may typically lie between 15 bar and 230 bar, depending on nozzle type and material, while the material pressure at the outlet of the metering device or of the metering pump, which is higher due to inevitable pressure losses, may amount in typical cases to between 25 bar and 350 bar and is thus considerably higher than in paint application systems. As a rule, the application system according to the exemplary illustrations is thus intended to operate with a material pressure of at least 15 bar at the application nozzle and/or at least 25 bar at the outlet of the metering device or metering pump.
Metering may be effected in a demand-dependent manner, i.e. during coating the volumetric flow rate (through-flow per unit time) of the coating material fed to the applicator has to be very precisely variable with short response times as a function of the respective sub-zones of the workpiece, the respective setpoints being saved in the higher-level installation control means and predetermined thereby. In many cases, metering accuracy should amount to at least ±1% of the setpoint, with good repeatability under temperature, viscosity and pressure fluctuations. Because of the level of accuracy needed, continuous volume control may be required. With sealing applications in particular, it is important to avoid pulsing during application. The components of the metering system must as far as possible be free of dead spaces, inter alia to avoid curing. Particular requirements apply when metering special coating materials such as for example NAD material (non-aqueous polymer dispersion), for which inter alia special measuring devices are needed, or with materials for which a high metering pressure is reached during application, for example up to 400 bar in the case of PU. Different conditions arise with regard to volumetric flow rate, i.e. flow rate, which may in typical cases amount to for example between 2 and 50 ccm/sec. Further requirements relate to the admissible rise and response times of the system (<40 ms to reach ±5% of the setpoint), freely programmable adjustability of the admission pressure with short response time (<100 ms) and automatic dynamic adaptation of the admission pressure in the event of changes in the viscosity of the coating material, the possibility of automatic calibration in the event of material changes and short delay times at the start of operation. In general, not only the costs of the installation and maintenance thereof but also the weight and dimensions of system components, in particular with respect to mounting in or an application robots, should be as low as possible.
If, for example, an application robot is to be used to seal a weld or edge-formed seam of the workpiece, application generally has to be controlled such that not only is the quantity of material required in each case precisely metered but also the predetermined start and end points of the material seam are precisely observed. Because of the in practice relatively rapid application movements of a robot, very precise control of application on and off times is necessary therefor.
In the field of vehicle body coating, it has in practice been conventional, unlike in paintshops, to use discontinuous metering devices to meter high viscosity coating compositions, or indeed “pressure regulators”, which are relatively light and may therefore also be mounted on the application robot. However, such devices generally operate with only low metering accuracy and at the same time with low metering dynamics or response rate. In addition, they are generally not capable of at least briefly increasing the pressure required at the application nozzle independently of the material supply in such a way as may in many cases be necessary, or of reducing the pressure prior to the start of application, as may likewise be necessary. Furthermore, discontinuous metering systems have further fundamental disadvantages such as refill time losses, long cycle times or a small metering range.
A metering system usable inter alia for sealants and adhesives is generally known from WO 2004/041444 and consists substantially of a continuous metering piston or gear pump and a second metering stage connected downstream thereof in the form of a cylinder container, the contents of which are held by a piston between two predetermined levels. Like other generally known piston metering devices, this metering system is so bulky and heavy, at least if sufficient metering precision is to be achieved, that it cannot be mounted on or in an application robot, because the load-carrying capacity thereof would be exceeded and/or its motion dynamics and in many cases the reachability of the workpiece areas to be coated, for example in the interior of a vehicle body, would be impaired. This has the significant disadvantage of undesirably long hose connections between the metering device and the applicator, with the consequence of a reduction in metering accuracy and metering dynamics, inter alia because of the known problems of hose “breathing”. Long hoses also have the further disadvantage of correspondingly high material losses during a rinsing or cleaning process or of material settling problems, in particular if the material is not constantly circulating as far as the applicator.
Robots and applicators suitable for the application of sealing material to vehicle bodies are also generally known inter alia from U.S. Pat. No. 6,053,434 and EP 1 521 642. The applicators of these robots consist substantially of a tubular lance part, on the outer end of which an arrangement of for example three alternatively selectable nozzles are located. For each nozzle a control valve for the material fed to the applicator from outside is fitted in the applicator, with which control valve (for instance corresponding to the main needle function of conventional paint atomisers) application on and off times and thus the start and end points of the applied material course are controlled.
The object of the present disclosure is to achieve the shortest possible connection between the metering device and the applicator and the precisest possible metering and application while avoiding the disadvantages of known systems for high viscosity material, e.g., without significantly impairing the movement machine with regard to load carrying capacity, motion dynamics and/or the reachability of the workpiece zones to be coated. It is intended to achieve these aims with the least possible cost.